Mr. Goodman on the Dissimilarity of Electricities. 1 75 



in its usual form at all times belong those attractive and repul- 

 sive properties which are displayed in the separation of the 

 gold leaves or pith-balls of an electroscope. In consequence 

 of the same it exhibits much elasticity of character and expan- 

 sive powers, great mechanical violence, momentum, and capa- 

 bility of resisting and opposing the pressure of the atmosphere, 

 and thus producing great passing distance and the appearance 

 of considerable magnitude of spark, &c. On the other hand, 

 the voltaic fluid produced by a single pair of plates exhibits 

 no sensibly attractive or repulsive properties, no mechanical 

 violence, &c. ; and so powerless is its current in opposing at- 

 mospheric pressure that it is incapable of exhibiting a single 

 spark, unless the plates are of considerable magnitude. Yet 

 with regard to quantity, the greatest amount of fluid which 

 could at any time be elicited from my electrical machine and 

 rendered available for decomposition of water (the most cer- 

 tain test of quantity), was calculated as equal to only 7 jth of 

 the current produced by a voltaic pair formed of zinc and 

 copper wire y^th inch in diameter. 



Now, although there exists this marked distinction between 

 the properties of the voltaic and ordinary electricities, there is 

 not in the English language a term in use by which any two 

 electricians can distinctly recognize the particular properties 

 of either fluid. There are indeed two terms which are pre- 

 cisely applicable to these conditions, viz. "tension and inten- 

 sity," but they are as yet used by electricians without any di- 

 stinction, and to express the same meaning. From their deri- 

 vation, however, tension from the verb tendo, to stretch or ex- 

 tend, and intensity from the preposition in and the same verb, 

 the application of the former to a stretching or extension out- 

 wards (which, as will shortly be seen, is the nature of the ordinary 

 electricity), to this condition the former may be very properly 

 applied. We have this term frequently applied in common 

 use to the stretching of a bowstring, the condition of a hoop 

 around a carriage wheel, that of the plates of a high-pressure 

 steam-boiler, or the cords of a musical instrument, to which 

 no one would for a moment think of applying the term " in- 

 tensity," whereas the latter, which is used commonly to denote 

 a state of being affected to a high degree, must be one to which 

 the condensation of quantity will be most fitly applicable. 

 We now come to the consideration, what is the cause, and in 

 what consists the difference between the voltaic and ordinary 

 electricities. The view which I have taken of the cause of 

 dissimilarity in the phaenomena of the two fluids is illustrated 

 in the employment of a condensing electrometer, or by the ac- 

 companying apparatus. 



